1. Field of the Invention
The present invention relates to silicon carbide (SiC) single crystal, a SiC substrate and a manufacturing method for SiC single crystal, and in particular, to p type SiC single crystal having high resistivity, a SiC substrate and a manufacturing method for SiC single crystal.
2. Description of the Background Art
SiC has a band gap that is approximately 3 times greater than that of silicon (Si), a dielectric breakdown voltage that is approximately 10 times higher than that of Si, an electron saturation speed that is approximately twice greater than that of Si, and thermal conductivity that is approximately 3 times greater than that of Si, as well as properties that Si does not have. In addition, SiC is a thermally and chemically stable semiconductor material, and on the basis of these properties, and, in recent years, has come to be expected to be applied to power devices that exceed the physical limit of Si devices, or to environment resistant devices that operate at a high temperatures.
In addition, in research relating to optical devices, gallium nitride (GaN) based materials have been developed, with shorter wavelengths in mind, and since lattice mismatch with GaN is remarkably small in SiC, in comparison with other compound semiconductors, SiC substrates have attracted attention as a substrate for epitaxially growing a GaN layer.
In this area of electronics, it is necessary to control the electronic conduction properties of a substrate in accordance with the purpose for use, and for example, a substrate having a low resistivity is required as a substrate for a semiconductor laser, and a substrate having high resistivity (semi-insulating properties) is required as a substrate for a high frequency device, so that the parasitic capacitance can be reduced, element isolation can be gained and the like.
A SiC substrate having low resistivity can be gained relatively easily, for example, by mixing a nitrogen gas with an argon gas, which is an atmospheric gas, in an improved Rayleigh method.
Meanwhile, a SiC substrate having high resistivity can be manufactured by cutting SiC single crystal containing vanadium and having high resistivity, as described in, for example, U.S. Pat. No. 5,611,955, PCT National Publication No. 2003-500321, and Japanese Patent Laying-Open No. 2003-104798. Such SiC single crystal containing vanadium and having high resistivity can be manufactured by adding highly pure metal vanadium to a highly pure SiC crystal powder, and by sublimating the metal vanadium together with SiC, so that vanadium is contained in the SiC single crystal.
The rate of sublimation of metal vanadium is high, however, and therefore, a great amount of vanadium is taken in by the SiC single crystal at the initial stage of the growth of the SiC single crystal, and thus, vanadium cannot be uniformly contained in the SiC single crystal. In addition, at the initial stage of growth, the amount of vanadium that is contained in the SiC single crystal exceeds the solubility limit, and at this point, deposition occurs and the crystallinity deteriorates, and therefore, deterioration in the crystallinity at this early stage of growth negatively affects the SiC single crystal that is grown afterwards. As a result of this, a problem arises, where SiC single crystal having high resistivity cannot be stably manufactured. In addition, a problem arises, where great dispersion is caused in the resistivity of a SiC substrate that is gained by cutting SiC single crystal.
As a means for solving this problem, Japanese Patent Laying-Open No. 2003-104798 discloses a method for manufacturing SiC crystal that contains vanadium in advance, and then converting it into powder form, and re-growing SiC single crystal that contains vanadium from this raw material in accordance with an improved Rayleigh method. In accordance with this method, however, it is necessary to manufacture SiC crystal that contains vanadium in advance, and therefore, a problem arises, where SiC single crystal having high resistivity cannot be efficiently manufactured.
In addition, a SiC substrate having high resistivity can be fabricated by increasing the purity of SiC single crystal instead of adding vanadium as described above. SiC single crystal that has been fabricated in accordance with a high temperature CVD method, which is a specialized chemical vapor deposition (CVD) method, for example, tends to have high purity. However, in order to gain highly pure SiC single crystal, it is necessary to preserve this high purity during the growing process (raw material, growing apparatus and the like), and it is very difficult to preserve high purity stably during the growing process.